© Shutterstock

Heterochromia -

This is a popular one, among the rare eye features, of course. Heterochromia is essentially when a person’s two eyes are not the same color. People are usually born like this, but it can also appear later in life, as a result of a disorder or an injury.

© Shutterstock

Heterochromia -

There are a few famous people who have different colors in their left and right irises. Actress Jane Seymour is one example: she has one green and one brown eye.

© Getty Images

Heterochromia -

Some people, however, have partial heterochromia. This is when both eyes are mostly the same color, except one of them has another color mixed in. Actor Henry Cavill, for instance, has blue eyes, but also has a shade of brown in his left eye.

© Getty Images

Polycoria -

Polycoria is when a person has more than one pupil in the eye. This can manifest in one or both eyes.

© Shutterstock

Polycoria -

People who have more than one pupil that works independently have true polycoria, whereas those who have an extra pupil that's functional have pseudopolycoria. Pseudopolycoria is essentially a hole in the iris, and often occurs as a result of trauma or a condition.

© Shutterstock

Polycoria -

While some people with polycoria don't experience a lot of symptoms, others may struggle with blurred vision and poor night vision.

© Shutterstock

Ocular albinism -

Ocular albinism occurs when there is an absence of pigmentation in the iris. Unlike some other features on this list, the absence of color in the eyes may cause some vision issues.

© Shutterstock

Ocular albinism -

Ocular albinism is the result of a genetic mutation. People who suffer from it tend to have light blue irises, and the lack of pigmentation in the retina can cause the eyes to have a violet or red hue.

© Shutterstock

Ocular albinism -

Because ocular albinism causes sensitivity to light, people who have it need to protect their eyes by wearing dark lenses.

© Shutterstock

Cat eye syndrome -

Cat eye syndrome (CES) is a rare chromosomal disorder. People who suffer from it are born with elongated pupils, similar to those of cats.

© Shutterstock

Cat eye syndrome -

Because it’s a chromosomal disorder, CES patients experience other issues in addition to the eyes, including potential problems with the lips, heart, ears, kidneys, and bones.

© Shutterstock

Coloboma -

This feature, which is sometimes mistaken for heterochromia or CES, develops when the embryo is in the womb. It can result in a number of missing eye parts, and it can affect one or both eyes.

© Shutterstock

Coloboma -

Different names are given for the condition, depending on which part is missing. For instance, a person may have eyelid coloboma, lens coloboma, or uveal coloboma (a partly-missing iris).

© Shutterstock

Coloboma -

Uveal coloboma in particular may cause a number of issues, including light sensitivity and blurry vision.

© Shutterstock

Anisocoria -

Anisocoria is when people have different sized pupils. Uneven pupils can be hereditary or be caused by trauma (injury) or conditions (e.g. stroke).

© Shutterstock

Anisocoria -

A famous example is late musician David Bowie. Following a fistfight as a teen, Bowie’s left pupil was left permanently dilated.

© Getty Images

Graves’ ophthalmopathy -

Graves' disease is an immune system condition where the body overproduces thyroid hormones. This leads to a number of symptoms, including an ocular condition known as Graves' ophthalmopathy.

© Shutterstock

Graves’ ophthalmopathy -

Graves’ ophthalmopathy symptoms include bulging eyes, light sensitivity, gritty eyes, and puffy eyelids.

© Shutterstock

Graves’ ophthalmopathy -

Missy Elliot is a famous example of someone who suffers from Graves’ ophthalmopathy.

© Getty Images

Waardenburg syndrome -

Waardenburg syndrome is a group of genetic conditions. Among other things, it can affect pigmentation, and therefore the coloring of the eyes.

© Shutterstock

Waardenburg syndrome -

Model and actress Paris Jackson is believed to have Waardenburg syndrome, hence her unique-looking blue eyes.

© Getty Images

Microphthalmia -

People with microphthalmia have smaller eyes than average. Unfortunately, this comes with some serious side effects, including partial vision loss or even blindness. The condition can affect one or both eyes.

© Shutterstock

Microphthalmia -

Those with microphthalmia have small eye sockets, so the eyeballs become misshapen as they develop. The root cause of the condition is not known, but genetics and environmental factors are often pointed to as causes.

© Shutterstock

Microphthalmia -

British actress Anna Cannings is one example of a person with microphthalmia. In Cannings’ particular case, she was born blind, with bilateral microphthalmia (both eyes were affected from birth).

© Getty Images

Chronic progressive external ophthalmoplegia (CPEO) -

Unlike other eye features on this list, chronic progressive external ophthalmoplegia (CPEO) develops later in life. A common symptom is a drooping eyelid.

© Shutterstock

Chronic progressive external ophthalmoplegia (CPEO) -

CPEO is caused by DNA mutations, which occur later in life, and can affect one or both eyes, as well as other areas of the body (e.g. muscle weakness, heart problems, etc.).

© Shutterstock

Distichiasis -

People with distichiasis have a second set of eyelashes that grow from the inner mucosal layer of the eye. This is caused by epithelial germ cells failing to differentiate between certain glands.

© Shutterstock 

Free-floating iris cyst -

A free-floating iris cyst is essentially an iris cyst that moves around in the anterior chamber. These manifest as a ball of color moving in the eye.

© Shutterstock

Free-floating iris cyst -

While free-floating iris cysts are mostly harmless, they can cause pain and lead to secondary glaucoma.

Sources: (American Academy of Ophthalmology) (Health Digest) (WebMD) (National Organization for Rare Disorders)

See also: What do your eyes say? Celebrities with different-colored eyes

© Shutterstock